Starting from an existing touch framework/application is not the problem.

"Porting" a desktop application to a touch application is not "just" (to quote polshaw) adding a new UI. There's a world of difference between a desktop GUI--esp. in the Linux world, where many apps are remarkably different due to the ecosystem--and a touch GUI. Touch target sizing, what information to get rid of (if any?), what to add, speed (arguably more important on a mobile device), hardware acceleration (read: being gentle on battery life & improving touch responsiveness)... it goes on.

The OS might have Ubuntu/Linux roots, but it doesn't automatically mean it gets a free ride to a great touch-friendly mobile app library.